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Trailer Axle Fitment Guide

How to Measure a Trailer Axle

Correct axle replacement starts with two measurements: Hub Face and Spring Center. Use this guide before ordering or calling about a replacement axle.

Start Measuring Search Axle Inventory

Two Measurements Matter Most

Most replacement beam axles are identified by Hub Face (HF) and Spring Center (SC). These dimensions tell us where the wheels sit and whether the axle will line up with your trailer suspension.

You will need:
  • Tape measure
  • Axle tag photo, if available
  • Hub face measurement
  • Spring center measurement
  • Bolt pattern and brake type

Beam / Idler Axle Measurement Example

This diagram shows where to measure Hub Face and Spring Center on a common idler trailer axle. Brake axles are measured the same way.

How to measure hub face and spring center on an idler trailer axle

Measurement 1

Hub Face Measurement (HF)

Hub Face is measured from the flat wheel-mounting face on one hub to the flat wheel-mounting face on the opposite hub.

This measurement determines where the wheels sit under the trailer.

Do not measure:
  • Tire outside to tire outside
  • Wheel edge to wheel edge
  • Overall axle length
  • Spindle tip to spindle tip

Measurement 2

Spring Center Measurement (SC)

Spring Center is measured from the center of one spring seat to the center of the opposite spring seat.

This measurement determines whether the axle lines up with your trailer leaf springs.

Measure center-to-center:
  • Center of left spring seat
  • Center of right spring seat
  • Not outside edge to outside edge
  • Not hanger spacing

Quick Estimate

Axle Capacity Estimator

Enter your trailer GVWR and axle count to estimate a common axle rating. This tool is limited to common trailer axle ratings up to 15,000 lb per axle. For heavier equipment, call for verification.

Idler, Electric Brake, and Hydraulic Brake Axles

Idler Axle

No brake components. Common on smaller trailers or non-braking axle positions.

Electric Brake Axle

Usually has brake backing plates and wiring at each brake assembly.

Hydraulic / Disc Brake Axle

May use calipers, rotors, hydraulic lines, or actuator-controlled braking.

Common Trailer Axle Measurement Mistakes

Measuring overall length

Overall axle length is not the same as Hub Face.

Measuring tire width

Tires and wheels can vary. Measure the hub mounting faces instead.

Confusing SC with hanger spacing

Spring Center is measured at the spring seats on the axle.

Ignoring brake type

Brake type, bolt pattern, and capacity must also match your application.

Before You Call

Have These Details Ready

  • Hub Face measurement
  • Spring Center measurement
  • Axle capacity, if known
  • Bolt pattern
  • Brake type: idler, electric, hydraulic drum, or hydraulic disc
  • Photos of axle tag, hubs, brakes, and spring seats

Need help identifying your axle?

Send photos and measurements or call R&P Carriages for fitment help.

Call 815-357-3292 Contact Us

Ready to Find a Replacement Axle?

Use your Hub Face and Spring Center measurements to search current inventory.

Search In-Stock Trailer Axles